Two types of projection display systems are digital light processor (DLP) systems, and liquid crystal display (LCD) systems. It is desirable in some projection applications to provide a high lumen level output, but it is very costly to provide such output levels in existing DLP and LCD projection systems. Three choices exist for applications where high lumen levels are desired: (1) high-output projectors; (2) tiled, low-output projectors; and (3) superimposed, low-output projectors.
When information requirements are modest, a single high-output projector is typically employed. This approach dominates digital cinema today, and the images typically have a nice appearance. High-output projectors have the lowest lumen value (i.e., lumens per dollar). The lumen value of high output projectors is less than half of that found in low-end projectors. If the high output projector fails, the screen goes black. Also, parts and service are available for high output projectors only via a specialized niche market.
Tiled projection can deliver very high resolution, but it is difficult to hide the seams separating tiles, and output is often reduced to produce uniform tiles. Tiled projection can deliver the most pixels of information. For applications where large pixel counts are desired, such as command and control, tiled projection is a common choice. Registration, color, and brightness must be carefully controlled in tiled projection. Matching color and brightness is accomplished by attenuating output, which costs lumens. If a single projector fails in a tiled projection system, the composite image is ruined.
Superimposed projection provides excellent fault tolerance and full brightness utilization, but resolution is typically compromised. Algorithms that seek to enhance resolution by offsetting multiple projection elements have been previously proposed. These methods assume simple shift offsets between projectors, use frequency domain analyses, and rely on heuristic methods to compute component sub-frames. The proposed systems do not generate optimal sub-frames in real-time, and do not take into account arbitrary relative geometric distortion between the component projectors.
Existing projection systems do not provide a cost effective solution for high lumen level (e.g., greater than about 10,000 lumens) applications. Existing projection systems also have a problem with projecting rich video and graphics content in real-time. The processing that is needed for delivering very good image quality and realistic graphics renderings is computationally intensive, and usually cannot keep up with real-time (e.g., video) frame rates. For this reason, such processing is typically replaced with much simpler algorithms that significantly compromise the quality of the rendered output.
Another problem with some existing projection systems, such as those used in many movie theaters, is that the systems do little or nothing to prevent illegal copying of the projected images. For example, a camcorder can be used in a movie theater to illegally record the projected images, and copies of the illegally recorded movie can then be sold to the public. Techniques have been proposed to help prevent such illegal copying, but many of these techniques adversely affect the quality of the projected images when viewed in the theater, and suffer from other disadvantages.